A ring laser gyroscope generally includes mirrors within centrally formed cavities for reflecting laser beams along the cavity length. A beam impinging upon a particular mirror will not be perfectly reflected due to normal irregularities on the surface of the mirrors. Rather, some back scattering occurs. This causes the beat frequency between two beams in the gyroscope to disappear at low inertial rotation input rates. This effect is referred to as lock-in which has been recognized for some time in the prior art and has been solved by driving the gyroscope body in rotational oscillation (dither). The means for accomplishing the dither conventionally includes a piezoelectric actuator connected to a suspension for the gyroscope which causes the body of the gyroscope to oscillate angularly at the suspension's natural mechanical resonant frequency. The dither is superimposed upon the actual rotation of the gyroscope in inertial space. The prior art includes various approaches to recover inertial rotation data free from dither and this does not form part of the present invention.
A number of torsional suspension systems have been devised for mounting a ring laser gyroscope so that it may be subjected to dither. One prior method for suspending the gyroscope utilizes two wagon wheel shaped torsional springs or hinges which are preloaded such that the gyroscope body is sandwiched between the hinges. Performance of such an assembly is less than optimum when subjected to a wide temperature range. Due to the mismatch between the coefficients of expansion of the materials of the hinge and the gyroscope body, as well as the high friction at the interfaces of the hinge and body, the problems of sticking/slipping occur. This results in erratic changes in path length along with large tilts leading to changes in gyroscope drift rate. Moreover, the large changes in path length with such a hinge design complicates the design of path length control transducers which must be employed to compensate for these path length changes.
A more recent prior art approach is to mount a wagon wheel torsional hinge within a central bore that is actually formed within the body of a ring laser gyroscope. Although such an arrangement has its advantages, expansion of the hinge material has been known to distort the gyroscope block and the path length with changes in temperature. Further, a wagon wheel torsional hinge configuration may lack sufficient material in the gyroscope block to counter sagittal tilt in response to thermal changes which will cause errors in the output of a gyroscope so equipped.